The present invention relates to a shadow-mask type color cathode-ray tube which is suitable for a color television tube, a color display tube for data processor, etc., especially, having a high resolution.
In the case of a shadow-mask type color cathode-ray tube in which the inner surface of the faceplate is flat and the shadow mask is also flat, the relative intervals between the electron beams which have reached the inner surface of the faceplate through the shadow mask apertures or slits are not constant, which causes what is called degrouping in the peripheral portion of the shadow mask. To reduce an error caused by degrouping, a method of making the pitch of the electron beam passing apertures larger in the peripheral portion of the shadow mask than in the central part thereof has been proposed, as described in Japanese Patent Laid-Open No. 942/1988. However, if the pitch of the shadow mask apertures is larger in the peripheral portion of the shadow mask than in the central portion thereof, defects such as deterioration of the resolution are produced. An error caused by degrouping is conventionally reduced by so designing the faceplate as to have a curved inner surface. In the prior art, in the case of the faceplate having a curved inner surface, the outer surface also has a curved surface so that the glass of the faceplate has a substantially uniform thickness.
On the other hand, a shadow mask which is set in the state of being stretched by tension, as described in Japanese Patent Laid-Open No. 942/1988, cannot generally have any other shape than a flat shape. In the case of a shadow mask having slit-type electron beam passing apertures, the shadow mask may have a cylindrical surface with the axis parallel to the slits.
If the faceplate has a flat outer surface, it is economically advantageous, because it is possible to use a flat glass plate as glass with a reflection reducing coating which is pasted to the outer surface of the faceplate and a flat touch panel is also usable.
However, no shadow-mask type color cathode-ray tube which has a faceplate with a flat outer surface and has a good characteristic as a cathode-ray tube has been known yet.